Some Bravais lattices have a particular geometry that can slow down the motion of Bloch electrons by pre-localization due to the band-structure properties. Another known source of electronic ...localization in solids is the Coulomb repulsion in partially filled d or f orbitals, which leads to the formation of local magnetic moments. The combination of these two effects is usually considered of little relevance to strongly correlated materials. Here we show that it represents, instead, the underlying physical mechanism in two of the most important ferromagnets: nickel and iron. In nickel, the van Hove singularity has an unexpected impact on the magnetism. As a result, the electron-electron scattering rate is linear in temperature, in violation of the conventional Landau theory of metals. This is true even at Earth's core pressures, at which iron is instead a good Fermi liquid. The importance of nickel in models of geomagnetism may have therefore to be reconsidered.
We study the impact of the valence and the geometry on the electronic structure and transport properties of different transition metal-benzene sandwich molecules bridging the tips of a Cu ...nanocontact. Our density-functional calculations show that the electronic transport properties of the molecules depend strongly on the molecular geometry which can be controlled by the nanocontact tips. Depending on the valence of the transition metal center certain molecules can be tuned in and out of half-metallic behaviour facilitating potential spintronics applications. We also discuss our results in the framework of an Anderson impurity model, indicating cases where the inclusion of local correlations alters the ground state qualitatively. For Co and V centered molecules we find indications of an orbital Kondo effect.
We study the origin of the temperature-induced Mott transition in Ca2RuO4. As a method we use the local-density approximation+dynamical mean-field theory. We show the following. (i) The Mott ...transition is driven by the change in structure from long to short c-axis layered perovskite (L-Pbca→S-Pbca); it occurs together with orbital order, which follows, rather than produces, the structural transition. (ii) In the metallic L-Pbca phase the orbital polarization is ∼0. (iii) In the insulating S-Pbca phase the lower energy orbital, ∼xy, is full. (iv) The spin-flip and pair-hopping Coulomb terms reduce the effective masses in the metallic phase. Our results indicate that a similar scenario applies to Ca2-xSrxRuO4 (x≤0.2). In the metallic x≤0.5 structures electrons are progressively transferred to the xz/yz bands with increasing x; however, we find no orbital-selective Mott transition down to ∼300 K.
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An intrinsic issue of the LDA
+
DMFT approach is the so called double counting of interaction terms. How to choose the double-counting potential in a manner that is both physically sound and ...consistent is unknown. We have conducted an extensive study of the charge-transfer system NiO in the LDA
+
DMFT framework using quantum Monte Carlo and exact diagonalization as impurity solvers. By explicitly treating the double-counting correction as an adjustable parameter we systematically investigated the effects of different choices for the double counting on the spectral function. Different methods for fixing the double counting can drive the result from Mott insulating to almost metallic. We propose a reasonable scheme for the determination of double-counting corrections for insulating systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The spin transition in LaCoO3 has been investigated using density-functional theory in combination with dynamical mean-field theory employing continuous time quantum Monte Carlo and exact ...diagonalization impurity solvers. Calculations on the experimental rhombohedral atomic structure with two Co sites per unit cell show that an independent treatment of the Co atoms results in a ground state with strong charge fluctuations induced by electronic correlations. Each atom shows a contribution from either a d5 or a d7 state in addition to the main d6 state. These states play a relevant role in the spin transition which can be understood as a low spin-high spin (LS-HS) transition with significant contributions (~10%) to the LS and HS states of d5 and d7 states, respectively. We report spectra as well as optical conductivity data for all cases. A thermodynamic analysis reveals a significant kinetic energy gain through introduction of charge fluctuations, which in addition to the potential energy reduction lowers the total energy of the system.
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We study a Co-benzene sandwich molecule bridging the tips of a Cu nanocontact as a realistic model of correlated molecular transport. To this end we employ a recently developed method for calculating ...the correlated electronic structure and transport properties of nanoscopic conductors. When the molecule is slightly compressed by the tips of the nanocontact the dynamic correlations originating from the strongly interacting Co 3d shell give rise to an orbital Kondo effect while the usual spin Kondo effect is suppressed due to Hund's rule coupling. This nontrivial Kondo effect produces a sharp and temperature-dependent Abrikosov-Suhl resonance in the spectral function at the Fermi level and a corresponding Fano line shape in the low bias conductance.
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Current methods for detecting disseminated tumor cells in the skeleton are limited by expense and technical complexity. We describe a simple and inexpensive method to quantify, with single cell ...sensitivity, human metastatic cancer in the mouse skeleton, concurrently with host gene expression, using TRIzol-based DNA/RNA extraction and Alu sequence qPCR amplification. This approach enables precise quantification of tumor cells and corresponding host gene expression during metastatic colonization in xenograft models.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
AGATA: mechanics and infrastructures Smith, R.; Menegazzo, R.; Aufranc, C. ...
European physical journal. A, Hadrons and nuclei,
07/2023, Volume:
59, Issue:
7
Journal Article
Peer reviewed
Open access
The successful operation of AGATA requires a complex mechanical support structure for the safe and reliable operation of the detectors. Three mechanical structures were designed for the scientific ...campaigns at LNL, GSI and GANIL, each accommodating an increasing number of detectors. The present phase of the project, to increase the number of detectors from 60 to 180 (the
4
π
spectrometer), required a new concept in mechanical support. The detectors also require a suite of associated instrumentation, infrastructures and good system design for their optimum performance. This includes the automatic liquid nitrogen filling system, high and low voltage power supplies, and a series of signal cables and distribution systems. A well-designed electromagnetic compatibility across all the sub-systems is essential. An additional requirement is an easily accessible database that records the status of the wide range of components utilised on the project. This article describes all aspects of the mechanics and infrastructures.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Chromium dioxide CrO2 belongs to a class of materials called ferromagnetic half-metals, whose peculiar aspect is that they act as a metal in one spin orientation and as a semiconductor or insulator ...in the opposite one. Despite numerous experimental and theoretical studies motivated by technologically important applications of this material in spintronics, its fundamental properties such as momentum-resolved electron dispersions and the Fermi surface have so far remained experimentally inaccessible because of metastability of its surface, which instantly reduces to amorphous Cr2O3 . In this work, we demonstrate that direct access to the native electronic structure of CrO2 can be achieved with soft-x-ray angle-resolved photoemission spectroscopy whose large probing depth penetrates through the Cr2O3 layer. For the first time, the electronic dispersions and Fermi surface of CrO2 are measured, which are fundamental prerequisites to solve the long debate on the nature of electronic correlations in this material. Since density functional theory augmented by a relatively weak local Coulomb repulsion gives an exhaustive description of our spectroscopic data, we rule out strong-coupling theories of CrO2 . Crucial for the correct interpretation of our experimental data in terms of the valence-band dispersions is the understanding of a nontrivial spectral response of CrO2 caused by interference effects in the photoemission process originating from the nonsymmorphic space group of the rutile crystal structure of CrO2 .
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Abstract Due to agriculture and logging, Costa Rica has lost many primary forests, making reforestation an important task. To judge the progress of reforestation, it is important to follow the ...reassembly of organismal communities within restored habitats. The COBIGA project near La Gamba, in the Golfo Dulce region of Costa Rica, aims at reforestation of lowland sites with native tree species. Ants, as ubiquitous and highly abundant terrestrial organisms, have a substantial influence on tropical ecosystems. The multiple roles include scavenging, predation, herbivory, and mutualistic interactions. We examined ant community responses to reveal the status of community regeneration and functional integrity. We compared the composition and diversity of the ant assemblages at three different age reforestation sites (2, 8, and 10 years old) with those at an old-growth forest as a reference site. By offering canned tuna fish at ground level along replicated transects, we observed 43 ant species representing six functional groups during the 2 months of sampling. Most of the observed ant species were omnivorous, but old-growth forests harbored a substantial number of other functional groups, such as generalized predators, arboreal predators, and arboreal omnivores. In contrast, the youngest reforestation site harbored a severely impoverished ant assemblage comprising mostly generalized polygynous and polydomous ant species from lower trophic levels. The within-site heterogeneity of the ant assemblages increased from the youngest to the oldest forest. In addition, our results show the importance of monitoring the progress of forest recovery to avoid the spread of invasive species into primary habitats.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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